Automatic propeller blade support



Oct. 4, 1949. G. T. LAMPTON 2,483,913

AUTOMATIC PROPELLER BLADE SUPPORT Filed March 3, 1945 ATTORNEY Patented Oct. 4, 1949 AUTOMATIC PROPELLER BLADE snrroa'r Glen T. Lamp'ton, West Hartford, Conn., assignor to United Aircraft Corporation, Hartford, Conn, a corporation of Delaware Application March 3, 1945, Serial N 0. 580,835

3 Claims. 1

This invention relates to a flexible propeller blade support particularly for use in an aircraft propeller of the type shown and claimed in an application of Glen T. Lampton and Donald W. Perin, Serial No. 580,834, filed con-currently herewith, that has the pitch angle of its blades automatically reduced as its thrust increases, so that the propeller, within limits, willbe self-regulating to maintain constant engine speed.

A primary object of this invention is a blade support which will provide the necessary flexibility in a simple structure.

Another object of the invention is a blade support comprising a central bundle of wires extending centrally and diametrically through the driving hub and axially within the blades.

A further object is the provision of bellmouthed, cable supporting ferrules within the hub and blades so that each blade may hinge about a point intermediate its length.

Other objects and advantages will be apparent from the specification and claims and from the drawing which illustrates what is now considered to be a preferred embodiment of the invention.

In the drawings,

Fig. 1 is a longitudinal sectional view through the principal parts of a propeller made in accordance with the present invention and,

Fig. 2 is a similar view, partly in section, taken on a plane at right angles to the plane of Fig. 1.

Referring more in detail to the figures of the drawing, there is shown a two-bladed propeller made in accordance with the present invention.

The blades I shown in the drawing are of conventional wooden construction and have an elongated ferrule l2 extending axially therein from their hub ends for a portion of their length, the inner end of the opening extending through the ferrule being bell-mouthed. Preferably, and as shown in the drawing, the ferrule I2 is threadedly connected to itsblade, the threads being so formed that they will have maximum gripping power with-in the material of which the blade is formed.

The driving hub M for the blades H1 is provided with an elongated sleeve l6 extending therethrough which in the two-bladed form of propeller shown in the drawing, may extend diame r cally through the center 9i 89 84 19 2 9f the hub. The opposite ends of theopening extending through the sleeve l E arebell-mouthed similarly to the ferrules l2. Extending through this sleeve It in the hub M and into the fer-rules l2 secured within the blades I0 is a central bundle of wire strands l8, these wires preferably being formed into a spirally wound cable. The outer ends of the cable'or strandsof wire It preferably may besecured within the ferrules l2 by solder ing, tinning, brazing, 'or otherwise securing the cable to the portion of the ferrule within which the opening is of uniform diameter, that is, beyondthe bell-mouth portion. For a purpose presently to be referred to, the cable may be wound with a helix of the opposite hand to the rotation of the blade; that is, for a propeller having a right hand rotation, the cable l8 would have a left hand helix.

The sleeve I6 is secured to the hub by clamping it thereto by means of a number of bolts 29;

in addition, there may be a transverse shear pin 22 provided extending through the hub I l and sleeve It by means of which the sleeve is locked in position. As shown in Fig. 2, the hub I4 is split and its opposite side portions are drawn together into frictional contact with the outer surface of the sleeve It.

The shear pin 22 is installed after horizontal balance of the propeller is obtained by shifting the entire blade assembly. It is apparent that if one blade is thrown from the propeller due to failure of the threads in the blade or by fatigue failure of the cable 18, the unbalanced centrifugal load will shear the pin 22 and pull the remainder of the blade assembly through the hub l4 so that both blades It will leave the hub substantially simultaneously. This will instantly remove the unbalanced condition before serious damage can be done to the engine or its mountings and leave the plane in condition so that the pilot may make a normal deadstick landing.

The centrifugal forces acting on the blades l0 serveto stretch and thus tend to slightly unwind the cable l8. Normally there is a pitch reducing moment in the propeller blades Ill due to centrifugal forces which, in the present instance, is balanced out by forces in shear acting within the wire cable I8 and by the reaction on the ball seat presently to be referred to. By using a left hand cable 3 for a right hand rotation propeller,

this reaction is used to advantage to reduce the load on the point of attachment of the blade at the inner end of the post for the reason that the unwinding of the cable tends to increase the propeller blade pitch,

By reason of the cable l8 extending through the sleeve IS in the hub l4 and through the ferrule I2 and the outer ends of the opening within the sleeve l6 being bell-mouthed and the inner ends of the ferrule l2 also being bell-mouthed, the blades 10 may flex within limited angles relative to their driving hub M in any direction. The cable l8, made up of numerous strands and located centrally and longitudinally of the blades, permits this angular adjustment of the blades with but slight torsional resistance. Also the bell-mouthing of the sleeve "[6 and the ferrules l2 permits flexing of the cable l8 over a material length so that stresses of the cable strands due to this flexing are kept relatively low.

To retain the blades ID in their positions relative to the hub l4, while permitting limited angular movement in the plane of rotation and in the direction of flight, the skirts of the blades I!) have collars 24 surrounding them preferably of resilient material such as rubber to suppress vibrations. Surrounding each of the resilient collars 24 is a two-part clamping member 26 having an inward radially extending post '28 adjacent the trailing edge of the blade ill. This post 28 at its outer end engages within a portion of the clamp formed by members 26 and at its inner end engages within an opening in a resilient sleeve housed within a portion of the hub. The blades mounted in this manner may deflect or tilt in the direction of flight causing the skirt of the blade to move slightly downstream.

The pivotal or hinge point at which the blade deflects or tilts is at or near the joint formed by the bell-mouth ends of the openings in the sleeve and ferrule. This point is at an intermediate portion of the blade and at a substantial radial distance from its center of rotation. This flexing movement of the blades l takes place while the trailing edge of the blade is held against movement by the substantially fixed position of the inner end of the post 28. This movement, therefore, results in the pitch of the blade being changed. The greater the deflection of the blade due to thrust of the blade, the more the pitch of the blade is changed.

As the cable I8 is wound with a left hand helix and the blade ID has a right hand rotation, the centrifugal forces acting on the blade tend to unwind the cable slightly, this reduces the pressure acting on the post 28 forming the fixed point of attachment of the blade to the hub [4.

For a given propeller design the upstream deflection of the blade may be computed with a reasonable degree of precision and thereafter the location of the point of attachment of the heel of the blade to the hub can be determined so that the change in pitch under differences in thrust is of such an amount that substantially constant engine speed can be maintained throughout the entire velocity range of the airplane at one throttle setting.

If the airplane exceeds its designed velocity as during a dive the propeller will automatically increase its pitch beyond its normal level flight value and will maintain constant propeller speed under this regime.

At reasonably constant values of V/nD, (where V equals velocity of the plane, n equals R. P. M. and D equals diameter of propeller) which exist during part throttle level flight of an aircraft,

the thrust torque and centrifugal loads will vary as the square of the engine speed. Since these forces are designed to be in equilibrium, it follows that the propeller will only change pitch in response to a change in altitude, and consequent change in forward velocity of the aircraft, and that the pitch will be independent of throttle position in level flight. The propeller, therefore, behaves substantially as a fixed pitch propeller under engine throttle changes in level flight.

If so desired, the design features can be predetermined and the point of attachment of the heel of theblade to the hub positioned so that propeller engine combination, instead of maintaining constant speed under all conditions of flight at a single throttle setting, will provide a high speed for take-off and a lower speed in level flight. With the propeller so adjusted and the throttle maintained-at full throttle position the propeller speed will slow down as the airplane gathers forward velocity during and after take-off thus providing a propeller which will automatically give the increased power desired for take-off. f.

' For further explanation of the operation of the propeller forming the subject matter of this application reference may be had to the companion application 580,834 in which the present applicant is one of the joint inventors.

It is to be understood that the invention is not limited to the specific embodiment herein illustrated and described, but may be used in other ways without departure from the spirit of the invention as defined by the following claims:

I claim:

1. A self regulating propeller comprising in combination, a central driving hub, aligned blades extending radially in opposite directions from said hub, and blade mounting means pivotally connecting said blades with said hub for movement about axes extending longitudinally and transversely of said blade, said mounting means comprising, an elongated sleeve secured in and extending diametrically through said hub, the ends of the opening extending through said sleeve being bell-mouthed ferrules aligned with said sleeve and extending centrally and longitudinally into said blades from their hub ends and secured therein, said ferrules at their hub ends being bell-mouthed, and a flexible cable, said cable extending longitudinally through and secured to said sleeve and having its ends extending into and secured to said ferrules beyond their bell-mouthed ends, said sleeve extending substantially the entire distance between said ferrules and terminating adjacent V the bellmouthed ends of said ferrules, and supporting said cable except adjacent said bell-mouthed ends whereby, said unsupported portion of said flexible cable provides transverse and longitudinal, pivotal, support for said blades and the support portion of said cable restrains transverse and longitudinal movement of adjacent portions of said sleeve and ferrules.

2. The propeller blade mounting means claimed in claim 1 in which the flexible cable is a multistrand helically wound cable.

3. In a self regulating propeller having a driving hub, and a plurality of blades, means for flexibly mounting said blades in the hub for limited movement in any transverse direction with respect to said hub, a central multi-strand flexible cable retaining said blades against radial outward movement and providing a pivotal support therefor, aligned ferrules secured within said REFERENCES CITED The following references are of record in the file of this patent:

Number Number 10 449,664 563,529

UNITED STATES PATENTS Name Date 'Dodge July 25, 1933 Prewitt Mar. 11, 1941' Chilton June 10, 1941 FOREIGN PATENTS Country Date Great Britain July 1, 1936 France Dec. 7, 1923 

